shed9":36dkr1i3 said:
AndyT":36dkr1i3 said:
Harbo":36dkr1i3 said:
I’ve read that freezing works too.
Rod
I've read it too, but I'm sceptical.
I too am sceptical of freezing especially of killing off any eggs.
Freezing does work, and there's plenty of evidence of its effectiveness, e.g., it's used commercially, and this surely wouldn't be the case if the method was ineffective. Below is an extract from the timber technology book,
Cut & Dried.
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There are several non-chemical methods used to control insects. For the woodworker, the two we are most likely to encounter are freezing and high heat treatment, although it’s possible we may come across other methods including radiation and gas treatments such as nitrogen, oxygen scavenging and carbon dioxide treatments. These gas treatments rely on the insect's need for oxygen to survive, and denying it to them by one method or another eventually kills them.
Freeze treatments to destroy insect pests, including eggs, grubs and larvae work best when the temperature drops rapidly. The target temperature should be reached within twenty four hours throughout the object to be most effective, not just the surrounding air temperature or the outer portions of the piece. Insects can adapt to slow changes in temperature much better than they can cope with relatively quick changes. The freezer must be capable of taking temperatures down to at least -18ºC (-0.4ºF) and then once the object has reached this temperature it has to be maintained for at least two weeks. If the freezer can maintain temperatures as low as –30ºC (-22ºF) the treatment period, once the necessary temperature is reached, can be as short as three days.
A difficulty to overcome using freeze treatments is maintaining the moisture content of the object being treated. Water migrates out of wood as atmospheric RH drops, and cold air has very low RH so water moves out of wood and it may become too dry. As was discussed briefly in Section 8, Seasoning, Drying or Conditioning of Wood, freeze drying is one method of seasoning timber. Small objects must be wrapped and sealed in plastic bags to help maintain moisture content levels, and if air can be evacuated from the bag prior to freezing, this further helps maintain the object’s moisture content. After treatment the wrapping needs to stay in place until the object properly reaches normal temperatures to prevent condensation onto it as this may cause damage to finishes and so on.
Even rather large furniture items such as tables and chairs can be treated successfully if they are bagged and frozen in a walk-in freezer. Relative humidity needs maintaining at a suitable level, typically approximately 50%, in order to maintain wood moisture content at roughly 10%. If the piece has a lot of decorative veneer or inlay there is a high risk of irretrievable damage to these parts so freeze treatment is very likely to be inappropriate. There may also be a risk of damage to the applied finish negating the possibility of using this form of treatment.
Freezing might also succeed if there is an infestation in unworked but seasoned wood at about 10% MC or below where the boards can be close or dead stacked, similarly plastic wrapped as a pack, and frozen. However, wood is a good insulator and a large stack of wood might take considerable time to reach the target temperature. In this case individual wrapping and stickering as for seasoning would significantly reduce the time required to freeze the wood.
Heat of 50ºC (122ºF) and higher, maintained for extended periods, kills most insects at all stages of their life cycle. As with freezing, holding the moisture content of the treated object at an appropriate level is vital. In the early 1990s the German Thermo Lignum company was a pioneer in developing insect pest control using a purpose built chamber system with temperature and humidity controls to prevent damage to treated objects. This system controls atmospheric RH at a set point decided by the customer [usually 50%] and raises temperatures to 52ºC (126ºF) in the chamber and treatment cycles last, on average, twenty four hours. House longhorn beetle is more tolerant and needs a temperature of 55˚C. Treatment times are therefore quicker than freezing and large furniture items can be treated effectively without the need for bagging.
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